Fix getting server id for listing instances

Just use 'server_id' from the instance response instead.

Story: 2008464
Task: 41496
Change-Id: Ib84dbd5fbd752ab7c7607ccb874663b01bfb7388

Author: lingxiankong

troveclient/osc/v1/database_instances.py

@@ -56,9 +56,6 @@ def get_instances_info(instances):
         if 'addresses' not in instance_info:
             instance_info['addresses'] = ''
 
-        if 'server' in instance_info:
-            instance_info['server_id'] = instance_info['server'].get('id')
-
         if 'operating_status' not in instance_info:
             # In case newer version python-troveclient is talking to older
             # version trove.

troveclient/tests/osc/v1/test_database_instances.py

@@ -109,6 +109,7 @@ def test_instance_list_all_projects(self):
                 },
                 "tenant_id": tenant_id,
                 "access": {"is_public": False, "allowed_cidrs": []},
+                "server_id": server_id,
                 'server': {
                     'id': server_id
                 }
@@ -157,6 +158,7 @@ def test_instance_list_for_project(self):
                 },
                 "tenant_id": tenant_id,
                 "access": {"is_public": False, "allowed_cidrs": []},
+                "server_id": server_id,
                 'server': {
                     'id': server_id
                 }